Method for the continuous preparation of polyamide prepolymers

Abstract

The present invention relates to a method for continuously preparing a polyamide prepolymer, the viscosity in solution of which is comprised between 0.25 dL/g and 0.70 dL/g, as measured according to ISO 307:2007 in m-cresol at 20° C., the method being characterized in that it comprises a step of polycondensation on the basis of one or more polyamide precursor monomers, said polycondensation step being carried out in a extruder comprising at least two co-rotating conveying screws, the at least one monomer being previously added therein in solid or liquid form without being dissolved in a solvent or in water, and said polycondensation step being carried out without extracting the water formed during said polycondensation.

The invention claimed is: 
     
         1 . A method for the continuous preparation of a polyamide prepolymer, the viscosity in solution of which is comprised between 0.25 dL/g and 0.70 dL/g, as measured according to ISO 307:2007 in m-cresol at 20° C.,
 said formulated polyamide prepolymer having a number-average molecular weight (Mn) less than 10,000 g/mol, as determined by calculation from the level of terminal functions determined by potentiometric titration in solution and the functionality of said prepolymers or by NMR assay or by size exclusion chromatography, 
 wherein it comprises a step of polycondensation from one or more polyamide precursor monomers, said polycondensation step being carried out in a single extruder comprising at least two co-rotating conveying screws, the said monomer(s) being previously added in solid or liquid form without dissolving in a solvent or in water, and said polycondensation step being carried out without extraction of the products formed, said extruder not having any degassing devices, or of a device for removing the polycondensation by-product(s) formed, consisting of an outlet on the outside at atmospheric pressure, or of an outlet connected to a device making it possible to create a low-pressure zone in the extruder. 
 
     
     
         2 . The method according to  claim 1 , wherein the average degree of polymerization (DPn) of the resulting polyamide is less than 50, as determined from the number-average molecular weight (Mn) of the polyamides according to the following formula:
     DPn=Mn/M 0  [Formula 1]
   with   Mn, the number-average molecular weight of the polyamide,   M0 the number-average molecular weight of the monomers.   
     
     
         3 . The method according to  claim 1 , wherein the polyamide is an aliphatic polyamide. 
     
     
         4 . The method according to  claim 3 , wherein the monomer(s) is (are) at least one C6 to C18. 
     
     
         5 . The method according to  claim 3 , wherein the monomer(s) is (are) at least one C6 to C18 lactams. 
     
     
         6 . The method according to  claim 3 , wherein the monomer(s) is (are) at least one C6 to C18 aliphatic diamine, and at least one C6 to C18 aliphatic dicarboxylic acid. 
     
     
         7 . The method according to  claim 1 , wherein the extruder is a twin-screw extruder with two co-rotating conveying screws. 
     
     
         8 . The method according to  claim 7 , wherein it is carried out at a temperature comprised between 220 and 340° C., preferentially comprised between 260 and 300° C. 
     
     
         9 . The method according to  claim 8 , wherein the residence time of the material in the extruder at the temperature comprised between 220 and 340° C. allows executing the polycondensation reaction so as to arrive at the desired average degree of polymerization, said residence time being greater than or equal to 1 minute. 
     
     
         10 . The method according to  claim 1 , wherein the extruder is an annular multi-screw extruder comprising at least 6 screws, that are co-rotating. 
     
     
         11 . The method according to  claim 10 , wherein the residence time of the material in the extruder at the temperature comprised between 220 and 340° C. allows executing the polycondensation reaction so as to arrive at the desired average degree of polymerization, said residence time being greater than or equal to 1 minute. 
     
     
         12 . The method according to  claim 7 , wherein the residence time of the material in the extruder is greater than or equal to 1 minute. 
     
     
         13 . The method according to  claim 1 , wherein at least one additive is added during the polycondensation in the extruder.